Load Blinder Setting - GE MiCOM P40 Agile Technical Manual

Application Notes
MiCOM P40 Agile P442, P444
The start-up of the high-speed algorithms are confirmed
Under such circumstances, the low voltage could not be explained by normal voltage
excursion tolerances on-load. A fault is definitely present on the phase in question, and it is
acceptable to override the blinder action and allow the distance zones to trip according to the
entire zone shape. The benefit is that the resistive coverage for faults near to the IED
location can be higher.
For security, it is highly recommended that the blinder is Enabled, especially for lines above
150 km (90 miles), to prevent non-harmonic low-frequency transients causing load
encroachment problems, and for any networks where power swings might be experienced.
The impedance blinder radius i.e. R<Blinder Lim/Cos ß, must lower than the worst-case
loading as shown in the figure below. This is often taken as 120% overloading in one line,
multiplied by two to account for increased loading during outages or fault clearance in an
adjacent parallel circuit. Then an additional allowance for measuring tolerances results in a
recommended setting typically 1/3rd of the rated full load current:
Figure 63: Load blinder setting
Z < (Rated phase voltage Vn)/(IFLC x 3) , Therefore;
R< Blinder Lim < (Rated phase voltage Vn * Cosß)/(IFLC x 3)
FLC = Full Load Current
When the load is at the worst-case power factor, it should remain below the beta setting. So,
if we assume a typical worst-case 0.85 power factor, then:
ß > Cos-1 (0.85) plus 15° margin > 47°
and to ensure that line faults are detected, ß < (Line Angle -15°).
In practice, an angle half way between the worst-case leading load angle, and the protected
line impedance angle, is often used.
The undervoltage setting" Load Blinder V< " must be lower than the lowest phase-neutral
voltage under heavy load flow and depressed system voltage conditions. The typical
maximum V< setting is 70% Vn.
Load Blinder V<
P44x/EN AP/Hb6
(AP) 5-93